From GeneReviews Overview
Primary coenzyme Q10 (CoQ10) deficiency is usually associated with multisystem involvement, including neurologic manifestations such as fatal neonatal encephalopathy with hypotonia; a late-onset slowly progressive multiple-system atrophy-like phenotype (neurodegeneration with autonomic failure and various combinations of parkinsonism and cerebellar ataxia, and pyramidal dysfunction); and dystonia, spasticity, seizures, and intellectual disability. Steroid-resistant nephrotic syndrome (SRNS), the hallmark renal manifestation, is often the initial manifestation either as isolated renal involvement that progresses to end-stage renal disease (ESRD), or associated with encephalopathy (seizures, stroke-like episodes, severe neurologic impairment) resulting in early death. Hypertrophic cardiomyopathy (HCM), retinopathy or optic atrophy, and sensorineural hearing loss can also be seen.

From OMIM
Primary coenzyme Q10 deficiency-4 (COQ10D4) is an autosomal recessive disorder characterized by childhood-onset of cerebellar ataxia and exercise intolerance. Some affected individuals develop seizures and have mild mental impairment, indicating variable severity. Oral coenzyme Q10 supplementation does not result in significant improvement of neurologic symptoms (summary by Mollet et al., 2008 and Lagier-Tourenne et al., 2008). For a general phenotypic description and a discussion of genetic heterogeneity of primary coenzyme Q10 deficiency, see COQ10D1 (607426).  http://www.omim.org/entry/612016